[Tutor] Type hint question

[Albert-Jan Roskam]

   On Sep 26, 2024 19:50, Oscar Benjamin via Tutor <tutor at python.org> wrote:

     On Thu, 26 Sept 2024 at 18:12, Albert-Jan Roskam
     <sjeik_appie at hotmail.com> wrote:
     >

     >
     >    n = try_int(" 1")
     >    I get this message:
     >    main.py:7: error: Incompatible return value type (got "int",
     expected "T")
     >    [return-value]
     >    main.py:7: error: "T" has no attribute "strip" [attr-defined]
     >    Found 2 errors in 1 file (checked 1 source file)

     Those errors are reasonable.

     You have declared the parameter and return types to both be T. That
     means that this should return the same type as the input although note
     that "type" here is not exactly the same as "type" in the usual Python
     sense although usually it means the same thing.

     You are calling the function with a string and it will return an int.
     This is not consistent with saying that the return type is the same

   ====
   Arrgh. Of course! How stupid of me. **** That makes perfect sense. Thank
   you.

     Personally I wouldn't use "EAFP" like this for TypeError. Catching the
     ValueError for a string whose value might not be valid seems
     reasonable but types I would check explicitly whether with a
     TypeChecker or isinstance() and I would only use isinstance() at the
     boundaries.

   ====
   Isn't try-except cheaper if the "except" is relatively rare? Also, I
   thought try/except wss considered to be more pythonic... but I don't know
   where I read that.